This invention relates to certain dihydropyridines which are useful in the treatment of allergic and inflammatory conditions in humans and animals.
A number of 1,4-dihydropyridines have been previously described as antiischaemic and antihypertensive agents. These compounds are able to inhibit the movement of calcium into cells and are thus active in the treatment or prevention of a variety of cardiac conditions or as antihypertensive agents. (See for example EP-A-100189.) However the compounds of the present invention are potent and selective antagonists of platelet activating factor and as such they have clinical utility in a quite different area, namely in the treatment of allergic and inflammatory conditions such as asthma and arthritis respectively.
Platelet activating factor (PAF) (1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine) is an ether phospholipid whose structure was first elucidated in 1979. It is produced by, released from and interacts with many pro-inflammatory cells, platelets and the kidney. In addition to potent platelet aggregating activity, PAF exhibits a wide spectrum of biological activities elicited either directly or via the release of other powerful mediators such as thromboxane A.sub.2 or the leukotrienes. In vitro, PAF stimulates the movement and aggregation of neutrophils and the release therefrom of tissue-damaging enzymes and oxygen radicals. These activities contribute to actions of PAF in vivo consistent with it playing a significant role in inflammatory and allergic responses. Thus, intradermal PAF has been shown to induce an inflammatory response, with associated pain, accumulation of inflammatory cells and increased vascular permeability, comparable with the allergic skin reaction following exposure to allergen. Similarly, both the acute bronchoconstriction and chronic inflammatory reactions elicited by allergens in asthma can be mimicked by intratracheal administration of PAF. Accordingly agents which antagonise the actions of PAF and consequently also prevent mediator release by PAF, will have clinical utility in the treatment of a variety of allergic inflammatory and hypersecretory conditions such as asthma, arthritis, rhinitis, bronchitis and urticaria.
In addition to the above, PAF has been implicated as being involved in a number of other medical conditions. Thus in circulatory shock, which is characterised by systemic hypotension, pulmonary hypertension and increased lung vascular permeability, the symptoms can be mimicked by infusion of PAF. This coupled with evidence showing that circulating PAF levels are increased by endotoxin infusion indicate that PAF is a prime mediator in certain forms of shock. Intravenous infusion of PAF at doses of 20-200 pmol kg.sup.-1 min.sup.-1 into rats results in the formation of extensive haemorrhagic erosions in the gastric mucosa and thus PAF is the most potent gastric ulcerogen yet described whose endogenous release may underlie or contribute to certain forms of gastric ulceration. Psoriasis is an inflammatory and proliferative disease characterised by skin lesions. PAF is pro-inflammatory and has been isolated from lesioned scale of psoriatic patients indicating PAF has a role in the disease of psoriasis. Also, increasing evidence supports a potential pathophysiological role for PAF in cardiovascular disease. Thus recent studies in angina patients show PAF is released during atrial pacing. Intracoronary injection of PAF in pigs induces a prolonged decrease in coronary flow and in guinea pig hearts it induces regional shunting and ischaemia. In addition, PAF has been shown to initiate thrombus formation in a mesenteric artery preparation, both when administered exogenously and when released endogenously. More recently PAF has been shown to play a role in brain ischaemia induced in animal models of stroke.
Thus the compounds of the invention, by virtue of their ability to antagonise the actions of PAF, will be of value in the treatment of the above conditions.